Levain, sourdough, starter...call it want you want — it is the secret to authentic, yeasty, artisan bread. San Francisco sourdough has, in a sense, given all sourdoughs a bad name, but most wild yeast starters are far milder and (to my palate) more pleasant as well.

When it comes to making a levain, there is as much superstition as science being spread around, and there are as many methods to create a levain as there are bakers. I suspect all of them work and all of them occasionally fail — the main difference is that some routines are more involved than others.

The nascent levain requires the most attention during its first couple of days, so if you're not around weekdays, make your apple water on Tuesday or Wednesday, and you can begin adding the flour on Saturday morning. I like to include a little whole wheat flour in the initial feedings, as it seems to give the starter a boost.
See below for full instructions.

Prepare the apple water:

Let 1 quart of tap water sit out overnight to remove any chlorine.

Look for a hazy apple, preferably from a farm stand (the haze is wild yeast). Cut the apple into 1-inch chunks, and place, along with the peel of a second apple, into a container with 1 cup of the water. (Cover and reserve the remaining water for later.)

Let the apple and water sit covered, at room temperature, for 3 days, stirring daily. The mixture should be foaming a bit and smell a little like cider by the third day.

Build the levain:

Day 1

Measure out 150 g of the apple water through a fine strainer and add 150 g of the flour mixture. Whip vigorously, scrape down the sides, and cover with a screen (a frying pan spatter screen is ideal) or cheesecloth.

Leave the levain at room temperature, whipping every few hours to incorporate air. It is important to keep the starter aerated during the first few days.

Day 2

Add 75 g of the reserved tap water and 75 g flour, whip, and leave at room temperature, covered as before, for another 24 hours, again whipping occasionally. You should see bubbles starting to form and the mixture increasing in bulk.

Day 3

Transfer levain to a clean 2-quart container. Avoid transferring any of the dried bits from the sides of the old container.

Add 75 g each of bread flour and reserved tap water, whip and cover as before.

If at any point of this process, the levain starts to smell a bit funky, discard half, replenish with flour and water and whip more frequently. If the levain seems limpid (not rising and bubbling), increase the frequency of feedings.

Day 4

Feed it once again, with the remaining 100 g of flour and 100 g water, let it sit at room temperature for 2 to 3 hours, and your levain should be ready for use, although it will continue to develop flavor over the next few weeks. You can either use it in bread today or go to the next step.

Cover with an airtight lid, store in refrigerator, and follow the care and feeding directions below.

Care and feeding of your levain

Like an infant, a levain gets easier to care for with age. Just observe the following guidelines:

Keep the levain in a covered container in the refrigerator.

For the first few weeks, feed twice a week as described in the next step; afterwards, a weekly feeding is sufficient.

To feed, stir thoroughly and discard about 250 g of levain. Replace with 125 g water (straight from the tap is fine at this point) and 125 g flour (unbleached bread or all-purpose), and whip with a spoon or plastic spatula. Leave the lid ajar (so gases can escape) at room temperature for 2 to 4 hours before tightly covering and returning to refrigerator.

If you are baking regularly, feeding is simply part of preparing the levain for the bread, and no other feeding is necessary. You should always feed the levain several hours or the night before making bread, so replenish with the amount of levain the recipe calls for, and you maintain a constant supply of fresh levain with no effort.

Occasionally clean out your container with hot water (never soap) to remove the crud that forms on the sides.

If you want a stronger levain, leave it out overnight once in a while, and feed with smaller "meals."

You may see a puddle of liquid forming on top, a product of fermentation. It can simply be stirred back in, but if you want to remove it, place the container of levain on your digital kitchen scale, and zero out. Pour off the liquid, return the levain to the scale and replenish with fresh water and just a little flour (in a ratio of about 3 to 1) until you're back at zero. Then feed as usual.